This application claims the priority of German application 196 29 229.8, filed Jul. 20, 1996, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a process for carrying out a braking operation, and more particularly, to a process in which the transfer of the driver's foot from the accelerator pedal in the direction of the brake pedal is sensed and, when the accelerator pedal return speed exceeds a threshold value and a transfer of the driver's foot is sensed, an automatic braking operation is triggered during which a brake pressure is built up in wheel brakes, and the triggering of the automatic braking operation triggering a first time sensing.
An automatic braking is described in Auto Motor und Sport, (p. 40, Motorsportpresse Stuttgart, Volume 12/1996, Mar. 31, 1996).
According to the general automatic braking process to which the present invention is directed, the return speed of the accelerator pedal exceeds a. threshold value and a transfer of the driver's foot from the accelerator pedal to the brake pedal is determined, so that an automatic braking operation is triggered during which a brake pressure is generated in the wheel brakes. The automatic braking operating is terminated when either a certain time has passed since the triggering of the braking operation or when an operation of the brake pedal by the driver occurs.
Furthermore, a process for implementing an automatic braking operation is described in DE 44 13 172 C1 during whose implementation a braking pressure is generated which is higher than a braking pressure which corresponds to the brake pedal position. The triggering of the automatic braking operation will then take place when the operating speed of the brake pedal exceeds a threshold value. The threshold value is adapted to the actual driving situation as a function of the succession of the pedal operations and of the type and method of their implementation. An automatic braking operation, as described in DE 44 13 172 C1, can be terminated, for example, by a termination criterion corresponding to DE 43 38 070 C1. Additional criteria for terminating an automatic braking operation are described in DE 43 25 940 C1. The teachings in these documents are incorporated herein.
Although the process to which the present application is directed initiates an automatic braking operation early, even before the operation of the braking pedal, it is not capable of supporting, in a critical driving situation, the buildup of a brake pressure during the operation of the brake pedal by the driver. A process described in DE 44 13 172 C1 is incapable of recognizing a dangerous situation before the operation of the brake pedal by the driver. Thus, in comparison to the process to which the present application is directed, time is lost for the braking pressure buildup in said described process.
It is, therefore, an object of the present invention to provide a process which ensure a support of the driver during the brake pedal operation in critical driving situations and also carries out a brake pressure buildup before the driver operates the brake pedal, or of preparing the buildup to such an extent that an accelerated brake pressure buildup is achieved with the braking operation by the driver in critical driving situations.
This object has been achieved according to the present invention by providing a method in which a quantity is sensed which represents the operation of the brake pedal, the gradient of the quantity representing the operation of the brake pedal is determined, and in that the automatic braking operation is terminated if the gradient of the quantity representing the operation of the brake pedal exceeds the threshold rise value not before the exceeding of a first time limit value by the first time sensing or the switching of the brake light switch from the inoperative into the operative switching position triggers a second time sensing, a quantity representing the operation of the brake pedal is sensed, the gradient of the quantity representing the operation of the brake pedal is determined, and in that the automatic braking operation is terminated when either the switching of the brake light switch does not take place before the exceeding of a first time limit value by the first time sensing. Alternatively, the method can provide that, if the gradient of the quantity representing the operation of the brake pedal exceeds a threshold rise value not before the exceeding of a second time limit value by the second time sensing or with the triggering of the automatic braking operation, a brake pressure is generated, the automatic braking operation being terminated with the exceeding of a first time limit value if previously a quantity representing the operation of the brake pedal has exceeded a threshold rise value. Similarly, with the termination of the cruise control, an automatic braking operation is triggered, a brake pressure being generated in the wheel brakes during the automatic braking operation which brake pressure corresponds to the application of the brake pads onto the brake disk.
After an automatic braking operation has been triggered, the process according to the present invention monitors whether the time derivation of a quantity representing the operation of the brake pedal exceeds a threshold rise value. The exceeding of the threshold rise value must take place within a certain time period after the triggering of the automatic braking operation. It can also be required that the exceeding of the threshold rise value also takes place within a defined time period after the switching of the brake light switch from its inoperative switching position (brake lights off, BLS=0) into its operative switching position (brake lights on; BLS=1). Thereby, the existence of whether a critical driving situation is reliably and advantageously determined. If this situation is recognized, the automatic braking operation is continued.
According to another of the above-mentioned embodiments, it is not required to sense the transfer of the driver's foot between the accelerator pedal and the brake pedal. The automatic braking operation will then be triggered only on the basis of the accelerator pedal return speed. This intervention also must be limited with respect to time so that unintentionally, the vehicle will not be braked too much.
In addition to the on-time operation of the brake pedal, a rise of the operating force of the brake pedal beyond an operating force threshold value can also be required in order to continue the automatic braking operation. It is particularly advantageous for the braking pressure in the wheel brakes to be limited so that the braking effect achieved before the operation of the brake remains low. In the case of critical driving situations, a shortening of the required braking distance will still be achieved because the easing play of the wheel brake cylinders can be overcome also without generating a braking effect. A further increase of the brake pressure can be generated by the buildup of brake pressure in the master brake lines.
According to various embodiments of the present invention, the pedal travel, the pedal operating speed, the operating force or the brake pressure in the master brake lines can be used as the quantity representing the brake pedal operation.
Additional embodiments of the present invention relate to the determination of the second time threshold value which concerns the time after the switching of the brake light switch and the determination of the threshold rise value.
Another of the above-described embodiments according to the present invention involve a process for triggering a corresponding automatic braking operation in the case of vehicles with a cruise control for controlling the vehicle speed independently of the operation of the brake pedal by the driver. In this case, the termination of the cruise control triggers the automatic braking operation. A predetermined vehicle deceleration is set, this vehicle deceleration preferably being achieved by an engine drag torque. Prior thereto, however, the easing play of the wheel brakes is overcome in that a brake pressure is set in the wheel brake cylinders which corresponds to the application of the brake pads to the brake disks. As a result, in the event of a subsequent braking, a shortening of the braking distance is achieved. This occurs particularly when, with a subsequent, possibly additional operation of the brake, a critical driving situation is recognized because of the fact that the gradient of a quantity representing the operation of the brake pedal exceeds a threshold value and the automatic braking operation is continued such that a higher brake pressure is set than that corresponding to the operation of the brake pedal.
Other advantageous embodiments of the present invention correspond to the brake pressure to be generated in the wheel brakes after the triggering of the automatic braking operation. This brake pressure can be limited to a defined extent or can be regulated such that the vehicle deceleration does not exceed a defined extent. These embodiments have the advantage that they limit the deceleration of the vehicle before the driver operates the brake pedal and therefore avoid an uncomfortable jerking of the vehicle when the automatic braking operation is terminated. In addition, the performance of the vehicle is easier to judge by the driver who is following.
Still other advantageous embodiments of the present invention provide the automatic braking operation after the threshold rise value has been exceeded. Accordingly, a brake pressure will then be generated in the wheel brakes which is higher than the brake pressure which corresponds to the position of the brake pedal. In particular, the generated brake pressure may be such that control of the brake pressure by an antilock system takes place at least on some of the wheels.